The use of hard coat stucco has been employed as a building material since literally ancient days. For stucco and plaster applications, a lath or mesh is typically applied to the surface of the wall or ceiling structure. This provides mechanical holding or keying for the unhardened stucco or plaster. Metal lath is often used as the reinforcement when stucco or plaster is applied over open frame construction, sheathed frame construction, or a solid base having a surface that might otherwise provide an unsatisfactory bond for the stucco or plaster. When applied over frame construction, one may employ base coats of plaster with a total thickness of approximately ⅜ inch to approximately ¾ inch to produce a solid base for a decorative finish coat. Metal lath reinforcement is also recommended for the application of stucco and plaster to old concrete or masonry walls, especially if the surface is lacking in compatibility with the base layer. There are also plastic laths available for the same purpose as metal lath.
According to the International Conference of Building Officials Acceptance Criteria for Cementitious Exterior Wall Coatings, AC 11, effective Oct. 1, 2002, and evaluation report NER-676, issued Jul. 1, 2003, wire fabric lath should be a minimum of No. 20 gauge, 1 inch (25.4 mm) (spacing) galvanized steel woven-wire fabric. The lath should be self-furred, or furred when applied over all substrates except unbacked polystyrene board. Metal lath has structural integrity, but if made of steel can corrode over time. The metal can also unfavorably react with the chemistry of the plaster or stucco. Hence, plastic or non-metal lath has gained popularity.
Stone veneer has also gained in popularity. Mounting of stone veneer using lath can present similar issues to that of plaster and stucco. A concern with the stone veneer, and even stucco, is that moisture can find its way behind the outer stone or stucco surface. This can present itself by way of hole penetrations in putting up the lath, and water condensing or otherwise migrating behind the lath.